This invention relates to a method of manufacturing a three-dimensional printed wiring board, and more particularly a method of manufacturing a three-dimensional printed wiring board having an insulating layer formed from a thermoplastic resin.
As a rigid board in which a conductor circuit is formed on one or both sides of a prepreg formed from glass cloth impregnated with an epoxy resin, a three-dimensional printed wiring board formed with a recess for housing pin and ball grids and LEDs is known. Such three-dimensional printed wiring boards are sometimes called PGA (pin-grid arrays) boards or BGA (ball-grid arrays) boards.
As shown in FIG. 5, in order to manufacture a three-dimensional printed wiring board 12 by forming a recess 11 in a rigid board 10, a male mold 13 of a predetermined shape in the form of a round or polygonal column called a punching mold is pressed against an intended area for mounting parts on the front surface of a rigid board 10, a female mold 14 called a die mold is pressed against the back of the rigid board 10, the rigid board is sandwiched between both molds for hot-pressing to form recesses 11 at required places on the rigid board 10 to make the printed wiring board three-dimensional.
Also, as shown in FIG. 6, another method is known in which cutting work called countersinking is done on the front surface of a rigid board 15 to form a recess 16 in an intended area for mounting parts to make the printed wiring board three-dimensional.
As a material for an insulating board of a three-dimensional printed wiring board, a thermoplastic saturated polyester resin is known. A manufacturing method in which during a step of crystallizing such a thermoplastic resin, an insulating board is hot-pressed into a predetermined bent or drawn shape is disclosed in Japanese patent publications 6-93536 and 7-101772.
But in manufacturing a three-dimensional wiring board using a thermoplastic saturated polyester resin for the material of an insulating board, there is a problem that the insulating board deforms around a conductor pattern during hot-pressing, and a force (residual stress) that tends to restore the deformed body to the original state acts on the deformed body. In an extreme case, deformation called xe2x80x9cwavingxe2x80x9d is locally caused.
Also, in manufacturing a conventional three-dimensional printed wiring board using a glass epoxy resin, control of the degree of crosslinking of the epoxy resin to the step of hot-press forming is difficult, so that it is impossible to manufacture satisfactory products in reliability and mass-productivity. Also, for a printed wiring board reinforced with glass cloth, its use is limited because of low flexibility.
Also another problem is that if a three-dimensional printed wiring board for mounting of parts for which soldering heat resistance is required or a three-dimensional printed wiring board for mere electric wiring is subjected to bending, a bending stress acts on a conductor of copper or aluminum rather than on an insulating board made from a resin that is low in elasticity, so that the conductor is liable to be cut.
Furthermore, with a conventional polyimide-family board material, heat-fusing a conductor foil reliably at a relatively low temperature is not an easy thing.
An object of this invention is to solve the above-mentioned problems and provide a strain-free three-dimensional printed wiring board by eliminating residual stresses from the wiring board that has been hot-pressed to make it three-dimensional in the manufacture of three-dimensional printed wiring board using a thermoplastic resin that has a good heat resistance.
Also, another object of this invention is to make it possible to reliably heat-fuse a conductor foil to a polyimide resin board at a relatively low temperature, and also to provide a method of manufacturing a three-dimensional printed wiring board in which an intended three-dimensional shape can be accurately formed by hot-pressing at a relatively low temperature, and to provide a three-dimensional printed wiring board that also has soldering heat resistance and chemical resistance.
A still another object of this invention is to provide a three-dimensional printed wiring board in which conductors are less likely to be cut even if bending work is done after a conductor circuit has been formed.
In order to solve the above objects, according to this invention, there is provided a method of manufacturing a three-dimensional printed wiring board, the method comprising the steps of providing a filmy insulator comprising a thermoplastic resin composition containing 65-35 wt % of a polyaryl ketone resin having a crystal-melting peak temperature of 260xc2x0 C. or over, and 35-65 wt % of an amorphous polyetherimide resin, and having a glass transition temperature as measured when the temperature is increased for differential scanning calorie measurement of 150-230xc2x0 C., superposing a conductor foil on one or both sides of the filmy insulator, heat-fusing the conductor foil so that the thermoplastic resin composition will satisfy the relation between the crystal-melting calorie xcex94 Hm and the crystallizing calorie xcex94 Hc as expressed by the following formula (I), etching the conductor foil to form a conductor circuit, and deforming the printed wiring circuit obtained three-dimensionally.
[(xcex94Hmxe2x88x92xcex94Hc)/xcex94Hm]xe2x89xa60.5xe2x80x83xe2x80x83(I):
If a protective film is provided so as to cover the conductor circuit before deforming such a printed wiring board three-dimensionally, bending stress will not concentrate on the conductor circuit, so that it is possible to manufacture a three-dimensional printed wiring board having a conductor circuit which is less likely to be cut.
In order to impart soldering heat resistance to the filmy insulator, in the above-described method, the printed wiring board formed with a conductor circuit is subjected to heat treatment so that the thermoplastic resin composition will satisfy the relation expressed by the following formula (II):
xe2x80x83[(xcex94Hmxe2x88x92xcex94Hc)/xcex94Hm]xe2x89xa70.7xe2x80x83xe2x80x83(II):
As the heat treatment, hot-press forming may be employed.
As the conductor foil to be laminated on one or both sides of the filmy insulator, a conductor foil having its surface roughened is preferably employed. As the polyaryl ketone resin, a polyetherether ketone resin is preferable.
In the method of manufacturing the three-dimensional printed wiring board of this invention, an insulating layer is formed which comprises a filmy insulator which contains predetermined amounts of a crystalline polyaryl ketone resin and an amorphous polyether imide resin. Due to excellent properties of these resins, the insulating layer has heat-fusability and soldering heat resistance, and also has flexibility, mechanical strength and electrical insulating properties normally required for a printed wiring board.
The thermoplastic resin composition after a conductive foil has been heat-fused satisfies the relation expressed by the formula (I), has a glass transition temperature of 150-230xc2x0 C., and the crystal-melting calorie xcex94 Hm and the crystallizing calorie xcex94 Hc produced by crystallization while the temperature is being increased satisfies the relation expressed by the formula (I). The progression of crystallization of the polyaryl ketone resin due to heating is adjusted within a suitable range.
The conductor foil heat-fused to one or both sides of the filmy insulator is strongly bonded due to the heat-fusability of the thermoplastic resin composition, so that a precision conductor circuit formed by etching the conductor foil is also strongly bonded and less likely to peel off. The use of a conductor foil having its surface roughened is preferable because the bond strength between the conductor circuit and the insulating layer increases.
In order to three-dimensionally deform the printed wiring board formed with a conductor circuit, bending work by external force or hot-press forming may be employed.
If hot-press forming is carried out to make it three-dimensional, with a protrusion pressed on a predetermined portion of the surface of the printed wiring board formed with a conductor circuit, a relatively low temperature of 250xc2x0 C. or lower, usually around 230xc2x0 C. may be employed for hot-pressing. At this time, if the relation expressed by the formula (I) is met, the thermoplastic resin will exceed the glass transition temperature (Tg), so that it is possible to locally form recesses with high accuracy.
The thermoplastic resin composition of the insulating layer of the three-dimensional printed wiring board thus manufactured exhibits crystallizability expressed by the above formula (II). This wiring board has a sufficient soldering heat resistance to withstand 260xc2x0 C. Also, the protrusions and recesses of the mold are precisely reproduced, so that a three-dimensional printed circuit board is manufactured which can reliably accommodate parts to be mounted.
As for the bonding between the filmy insulator and the conductor foil, since they are heat-fused together without any adhesive such as expoxy resin between layers, various properties such as heat resistance, chemical resistance and electrical properties are not governed by the properties of an adhesive. Thus it is possible to make best use of various excellent properties of the insulating layer.
Also, since the application of an adhesive or cutting work to form recesses is not needed during the manufacturing steps, the manufacturing process is simplified. This provides an efficient manufacturing method of a three-dimensional printed wiring board.